The present invention relates to polymer blends and, in particular, blends of polymers, which are immiscible, and compatibilizing agents use therein.
The polymer industry is constantly searching for new polymeric materials. The mixing together of two or more polymers has been found to be a successful means of forming new property combinations without having to synthesize novel structures. However, a major problem encountered when two polymers are mixed is that, in the majority of combinations, the components tend to phase-separate to form heterogeneous mixtures that do not exhibit enhanced properties. Only in a limited number of cases do amorphous polymers blend to form one-phase mixtures. The term miscible as used herein describes a mixture of two or more polymers, which form a single-phase (solid or liquid) solution. The term immiscible is used to describe a mixture of two or more polymers, which cannot be uniformly mixed or blended to form a single-phase (solid or liquid) solution. Polymers, which can be mixed to form a miscible blend, are referred to as compatible.
Immiscible polymer blends with potentially useful properties must be compatible in order to be used in most applications. Compatible and incompatible refer to the degree of intimacy of blends. From a practical standpoint, it is useful to refer to a polymer blend as compatible when it does not exhibit substantial polymer segregation (i.e., demixing of the components of the blend). Such blends are referred to herein as miscible polymer blends. A blend that is heterogeneous on a macroscopic level would therefore be considered incompatible. The simple observation that a blend is compatible is sufficient to establish the material as potentially useful. Numerous techniques are used to determine if a polymer is single phase or multiphase. A quick but not totally reliable method is by transparency. Erroneous conclusions may be reached by this method if the refractive indexes of two polymers are similar. Microscopy is a more accurate tool for determining if a blend is single phase or multiphase. The glass transition temperature (Tg) of the individual polymers in the blend and the glass transition temperature of the blend itself provide insight into the nature of the blend. The glass transition temperature is the temperature at which the molecular chains have sufficient energy to overcome attractive forces and move vibrationally and transitionally.
Most polymer films are composed of two or more polymers, which are blended in order to achieve desired properties of lubrication, dielectric constant, adhesion, etc. Since polymer blends are often not miscible, phase segregation between the polymer components can be a significant problem, especially in thin films. A variety of industries, which use polymer blend films, are affected by phase segregation. For example, in microlithographic applications, phase segregation of blend films degrades the printing resolution. When blend films are used as lubricants in low tolerance magnetic disks, phase segregation can increase the aspect ratio of the film so that it exceeds the spatial tolerance. If the film is used as a lubricant or adhesive, phase segregation can degrade the quality and characteristics of the film. Also, if the film is used in color printing, phase segregation adversely affects the image quality and reproduction of color.
Block copoymers, which act as surfactants are commonly used to compatibilize films. However, they have numerous disadvantages: 1) they are expensive and complicated to synthesize; 2) they tend to form micelles rather than localize at the interface, and hence their efficiency is low; and 3) they are very system specific.
Organic solvents are used in industry as compatibilizers for hydrophobic polymers. These solvents are often aromatic and can pose a health hazard and a threat to the environment when they are disposed. As a consequence, industry is increasingly switching to less hazardous, water soluble polymers, or polymers that can be processed in supercritical fluids. The present invention provides a safe alternative to the solvents presently being used since its primary component is clay.
The present invention is a polymer blend composition including a first polymer and a second polymer, which are immiscible, and a compatibilizer. The compatibilizer includes an organoclay, which has been functionalized by an intercalation agent, whereby it has an affinity for each of the polymers. The intercalation agent is a reaction product of a polyamine and an alkyl halide in a polar solvent. The preferred alkyl halides are alkyl chloride and alkyl bromide and the preferred polar solvents are water, toluene, tetrahydrofuran, and dimethylformamide.
The first polymer and the second polymer can be a polystyrene, a polyester, a nylon, a polyolefin, an acrylic resin, a vinyl polymer, a polyalkylene oxide, such as polyethylene oxide, or an ionomer, such as a sulfonated polystyrene or a sulfonated polyolefin.
The present invention is also a method for making a thin film and the film products produced thereby. The method includes combining a first polymer and a second polymer that are immiscible and a compatibizer to form a miscible polymer blend. The compatibilizer includes an organoclay functionalized with an intercalation agent, wherein the intercalation agent is a reaction product of a polyamine and an alkyl halide in a polar solvent. The first polymer has a first glass transition temperature and the second polymer has a second glass transition temperature. The compatibilized polymer blend is then formed into a film, preferably by a spin cast method and on a silicon wafer. In a preferred embodiment, the first polymer, the second polymer and the compatibilizer are combined in a solvent, such as water, toluene, tetrahydrofuran or dimethylformamide.
Films formed from the miscible polymer blends of the present invention have a thickness of from about 25 nm (xe2x80x9cnanometersxe2x80x9d) to about 1,000 nm, preferably from about 50 nm to about 300 nm. The films formed from the compatibilized polymer blend can then be annealed at a temperature above the glass transition temperatures of the first and second polymers to enhance the properties of the film and the degree of compatibilization.
The nanocomposite compatibilizers of the present invention are more economical than block copolymers ($1.00 or less versus $1,000.00 or more per pound) and provide greater versatility. Another advantage of the present invention is that both the hydrophobic and hydrophilic surface functionalized clays, which are used in the nanocomposite compatibilizers, are available commercially. Consequently, both water-soluble and insoluble polymers can be compatibilized by this method. This versatility is not possible with the surfactants, which are now being used.